Real solutions MCQs With Answer

Real solutions MCQs With Answer are essential study aids for B. Pharm students mastering solution behavior, colligative properties, and non-ideal mixing. This concise, exam-focused collection covers Raoult’s law, vapor–liquid equilibrium, activity and activity coefficients, azeotropes, boiling point elevation, freezing point depression, osmotic pressure, partial molar properties, and deviations from ideality. Each question links theory to pharmaceutical applications like solvent selection, formulation stability, and concentration effects on drug delivery. The balanced mix of conceptual and calculation-based items reinforces understanding and builds practical problem-solving skills. Clear answers and focused rationales help you prepare for university exams and competitive tests. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What defines a real solution compared to an ideal solution?

• Solution in which intermolecular interactions are identical to pure components
• Solution showing measurable deviations from Raoult’s law or volume/enthalpy change on mixing
• Solution that obeys Henry’s law at all concentrations
• Solution with constant boiling point regardless of composition

Correct Answer: Solution showing measurable deviations from Raoult’s law or volume/enthalpy change on mixing

Q2. Raoult’s law is strictly valid for which type of solution?

• Real solutions with ionic solutes
• Ideal solutions where interactions between unlike molecules equal those between like molecules
• All dilute aqueous solutions
• Solutions exhibiting azeotropic behavior

Correct Answer: Ideal solutions where interactions between unlike molecules equal those between like molecules

Q3. A positive deviation from Raoult’s law indicates which of the following?

• Observed vapor pressure lower than predicted by Raoult’s law
• No change in volume on mixing
• Observed vapor pressure higher than predicted due to weaker solute–solvent attractions
• Complete immiscibility of components

Correct Answer: Observed vapor pressure higher than predicted due to weaker solute–solvent attractions

Q4. Which statement best describes negative deviation from Raoult’s law?

• Stronger attractive interactions between unlike molecules lead to lower vapor pressure
• There is an increase in vapor pressure due to repulsion
• Activity coefficients are greater than one
• The mixture forms a maximum boiling azeotrope only

Correct Answer: Stronger attractive interactions between unlike molecules lead to lower vapor pressure

Q5. What is an azeotrope?

• A solution with ideal behavior at all compositions
• A mixture whose liquid and vapor compositions are identical at a given temperature and pressure
• A nonvolatile solute dissolved in a solvent
• A solution that obeys Henry’s law exactly

Correct Answer: A mixture whose liquid and vapor compositions are identical at a given temperature and pressure

Q6. Which colligative property equation relates boiling point elevation to molality?

• ΔTb = Kf · m
• ΔTb = Kb · m
• ΔTf = Kb · m
• π = MRT

Correct Answer: ΔTb = Kb · m

Q7. Freezing point depression is expressed by which formula?

• ΔTf = Kf · m
• ΔTf = Kb · m
• π = iMRT
• ΔP = xsolute · P°solvent

Correct Answer: ΔTf = Kf · m

Q8. Which expression gives osmotic pressure for a dilute solution?

• π = Kb · m
• π = iMRT
• π = ΔTf / Kf
• π = xsolute · P°solvent

Correct Answer: π = iMRT

Q9. The van’t Hoff factor (i) accounts for what effect?

• Temperature dependence of vapor pressure
• Number of particles produced by solute dissociation or association
• Change in solvent polarity on mixing
• Activity coefficient variation with pressure

Correct Answer: Number of particles produced by solute dissociation or association

Q10. Which of the following is NOT a colligative property?

• Vapor pressure lowering
• Boiling point elevation
• Freezing point depression
• Surface tension change

Correct Answer: Surface tension change

Q11. For a nonvolatile solute in an ideal solution, vapor pressure lowering (ΔP) is proportional to:

• Molarity of solute
• Mole fraction of solvent
• Mole fraction of solute multiplied by vapor pressure of pure solvent
• Activity coefficient of solvent only

Correct Answer: Mole fraction of solute multiplied by vapor pressure of pure solvent

Q12. What is the partial molar property of a component in a mixture?

• The total property divided by number of components
• The change in an extensive property when one mole of that component is added at constant T, P and composition of others
• The property of the pure component at the same temperature
• Always equal to the molar property of the pure substance

Correct Answer: The change in an extensive property when one mole of that component is added at constant T, P and composition of others

Q13. Activity (a) of a component in solution is related to mole fraction (x) how?

• a = x / γ
• a = γ + x
• a = γ · x
• a = ln(γx)

Correct Answer: a = γ · x

Q14. Henry’s law is most applicable to which situation?

• High-pressure gas solubility in concentrated solutions
• Dilute solutions where solute behaves as ideal solute with gas phase
• Liquid mixtures showing strong hydrogen bonding
• All vapor-liquid systems regardless of composition

Correct Answer: Dilute solutions where solute behaves as ideal solute with gas phase

Q15. The Gibbs–Duhem equation expresses which relation?

• Sum of mole fractions equals one
• Interdependence of partial molar properties so they cannot vary independently
• Relationship between boiling and freezing points
• Direct proportionality of activity and concentration

Correct Answer: Interdependence of partial molar properties so they cannot vary independently

Q16. Which mixture is likely to form a maximum boiling azeotrope?

• Components with weaker A–B interactions than A–A and B–B
• Components with stronger A–B interactions than A–A and B–B
• Completely immiscible liquids
• Ideal mixtures at all compositions

Correct Answer: Components with stronger A–B interactions than A–A and B–B

Q17. An ideal solution is characterized by which of the following on mixing?

• Non-zero enthalpy and volume changes
• Zero enthalpy and zero volume change on mixing
• Formation of azeotropes only
• Complete dissociation of solute molecules

Correct Answer: Zero enthalpy and zero volume change on mixing

Q18. A positive excess Gibbs energy (G^E > 0) indicates:

• Behavior identical to an ideal solution
• Negative deviation from Raoult’s law
• Positive deviation from ideality and likely higher vapor pressure
• That the solution forms a minimum boiling azeotrope

Correct Answer: Positive deviation from ideality and likely higher vapor pressure

Q19. Why is distillation of a mixture containing an azeotrope problematic?

• Azeotropes have extremely low vapor pressures
• The liquid and vapor have the same composition at the azeotropic point, preventing further separation by simple distillation
• They decompose on heating
• Azeotropes always form solids during distillation

Correct Answer: The liquid and vapor have the same composition at the azeotropic point, preventing further separation by simple distillation

Q20. Which expression gives the chemical potential of a component in solution?

• μi = μi° + RT ln xi
• μi = μi° + RT ln ai
• μi = μi° + Ki · m
• μi = μi° + γi

Correct Answer: μi = μi° + RT ln ai

Q21. For an ideal binary liquid mixture at equilibrium, the partial pressure of component A is given by:

• PA = yA · Ptotal
• PA = xA · P°A
• PA = kH · xA
• PA = γA · xA · P°A

Correct Answer: PA = xA · P°A

Q22. Adding a nonvolatile solute to a solvent will:

• Lower the solution’s boiling point
• Increase the solution’s vapor pressure above the pure solvent
• Elevate the boiling point of the solution compared to the pure solvent
• Have no effect on vapor pressure or boiling point

Correct Answer: Elevate the boiling point of the solution compared to the pure solvent

Q23. Which statement is correct for freezing point depression?

• ΔTf is independent of the number of solute particles
• ΔTf is proportional to the molality of solute particles and Kf of the solvent
• ΔTf increases with decreasing van’t Hoff factor
• Freezing point depression applies only to electrolytes

Correct Answer: ΔTf is proportional to the molality of solute particles and Kf of the solvent

Q24. How do electrolytes affect colligative properties compared to non-electrolytes?

• They have no effect because colligative properties depend only on solvent
• They reduce the magnitude of colligative effects
• They amplify colligative effects proportionally to the number of ions produced (considering ion association)
• They invert the sign of colligative property changes

Correct Answer: They amplify colligative effects proportionally to the number of ions produced (considering ion association)

Q25. In dilute solutions the solvent typically obeys Raoult’s law while the solute obeys which law?

• Henry’s law
• Van’t Hoff law
• Gibbs–Duhem law
• Dalton’s law

Correct Answer: Henry’s law

Q26. Activity coefficients (γ) approach unity under what condition?

• Strongly non-ideal concentrated solutions
• High-pressure gas mixtures
• Ideal solutions or very dilute solutions where behavior approximates ideality
• Only for ionic solutions at high ionic strength

Correct Answer: Ideal solutions or very dilute solutions where behavior approximates ideality

Q27. Which property is zero for an ideal solution?

• Excess Gibbs free energy (G^E)
• Mole fraction of solvent
• Pure component vapor pressure
• Activity coefficient

Correct Answer: Excess Gibbs free energy (G^E)

Q28. Which relation expresses the dependence of vapor pressure of a component in a mixture on its mole fraction for an ideal solution?

• Pi = yi · Ptotal
• Pi = xi · P°i
• Pi = γi · xi
• Pi = kH · xi

Correct Answer: Pi = xi · P°i

Q29. Which of the following increases the osmotic pressure of a solution at constant temperature?

• Decreasing solute concentration
• Increasing solute concentration
• Decreasing solvent density
• Changing solute to a less dissociating electrolyte without changing molality

Correct Answer: Increasing solute concentration

Q30. Minimum boiling azeotropes are typically associated with which deviation?

• Negative deviation from Raoult’s law
• Positive deviation from Raoult’s law
• Exactly ideal behavior
• Complete immiscibility

Correct Answer: Positive deviation from Raoult’s law

Q31. Which experimental observation indicates non-ideal mixing?

• No change in refractive index on mixing
• Measured enthalpy of mixing equals zero
• Volume contraction or expansion on mixing
• Perfect linear dependence of vapor pressure on composition

Correct Answer: Volume contraction or expansion on mixing

Q32. Debye–Hückel theory is used to estimate which quantity in electrolyte solutions?

• Boiling point elevation constant
• Activity coefficients at low ionic strength
• Molar mass of non-electrolytes
• Mole fraction of solvent

Correct Answer: Activity coefficients at low ionic strength

Q33. The relation μi = μi° + RT ln ai implies that if ai increases then:

• Chemical potential μi decreases
• Chemical potential μi increases
• Chemical potential is independent of activity
• Chemical potential becomes equal to μi°

Correct Answer: Chemical potential μi increases

Q34. In vapor-liquid equilibrium for an ideal binary mixture, the vapor phase is enriched in which component?

• The less volatile component
• The more volatile component
• Both components equally regardless of composition
• The component with higher molar mass only

Correct Answer: The more volatile component

Q35. Partial vapor pressure of a solvent in a dilute solution with a nonvolatile solute is approximately equal to:

• Psolvent = xsolute · P°solvent
• Psolvent = xsolvent · P°solvent
• Psolvent = P°solvent / xsolvent
• Psolvent = kH · xsolute

Correct Answer: Psolvent = xsolvent · P°solvent

Q36. Which quantity remains essentially independent of temperature and is used in freezing point calculations?

• Molality of solution
• Molar volume of solvent
• Mole fraction of solute
• Vapor pressure of solute

Correct Answer: Molality of solution

Q37. The presence of strong hydrogen bonding between unlike molecules typically causes:

• Positive deviation from ideality and increased vapor pressure
• Negative deviation from ideality and decreased vapor pressure
• No change from ideal behavior
• Formation of ideal azeotropes only

Correct Answer: Negative deviation from ideality and decreased vapor pressure

Q38. Which of the following is used to determine molar mass of a solute by freezing point depression?

• ΔTb and Kb
• ΔTf and Kf
• π and R
• P° and x

Correct Answer: ΔTf and Kf

Q39. Why is molality preferred over molarity for colligative property calculations?

• Molality depends on solution volume which changes with temperature
• Molality is temperature independent because it is based on mass of solvent
• Molality accounts for ionic dissociation automatically
• Molality gives the same numeric value as mole fraction

Correct Answer: Molality is temperature independent because it is based on mass of solvent

Q40. For a binary ideal solution, which of the following is TRUE about activity coefficients?

• Both γA and γB are equal to zero
• Both γA and γB are equal to one
• They vary linearly with temperature only
• They are always greater than one

Correct Answer: Both γA and γB are equal to one

Q41. Raoult’s law fails badly when:

• Solute and solvent are chemically identical
• Strong specific interactions (e.g., hydrogen bonding) occur between unlike molecules
• The solution is infinitely dilute
• Both components are ideal gases

Correct Answer: Strong specific interactions (e.g., hydrogen bonding) occur between unlike molecules

Q42. In a dilute solution with a nonvolatile solute, the solution vapor pressure P equals:

• P = xsolute · P°solute
• P = xsolvent · P°solvent
• P = P°solvent + P°solute
• P = kH · xsolute

Correct Answer: P = xsolvent · P°solvent

Q43. Which excess property is zero for an ideal solution?

• Excess volume
• Pure component vapor pressure
• Temperature of mixture
• Mole fraction

Correct Answer: Excess volume

Q44. If an activity coefficient γ > 1 for a component, it generally indicates:

• Negative deviation and stronger A–B attraction
• Positive deviation and weaker A–B attraction relative to ideal
• Ideal behavior
• Formation of a maximum boiling azeotrope only

Correct Answer: Positive deviation and weaker A–B attraction relative to ideal

Q45. Which statement about azeotropes is correct?

• Azeotropes always boil at the same temperature as the pure components
• Azeotropes can be separated into pure components by simple distillation
• Azeotropes behave as a single substance during boiling since liquid and vapor compositions are equal
• Azeotropes occur only in ideal solutions

Correct Answer: Azeotropes behave as a single substance during boiling since liquid and vapor compositions are equal

Q46. Which factor reduces the observed van’t Hoff factor of a strong electrolyte in solution?

• Complete dissociation at all concentrations
• Ion pairing or association at higher concentrations
• Lower solvent polarity always increases i
• Presence of a nonvolatile solute that does not dissociate

Correct Answer: Ion pairing or association at higher concentrations

Q47. Vapor pressure lowering for a dilute solution is equal to:

• ΔP = P°solvent / xsolute
• ΔP = xsolute · P°solvent
• ΔP = Kf · m
• ΔP = π / RT

Correct Answer: ΔP = xsolute · P°solvent

Q48. Which constant is specific to a solvent and used in boiling/freezing point calculations?

• Henry’s constant (kH)
• Ebullioscopic and cryoscopic constants (Kb and Kf)
• Activity coefficient (γ)
• Van’t Hoff factor (i)

Correct Answer: Ebullioscopic and cryoscopic constants (Kb and Kf)

Q49. For NaCl in dilute aqueous solution the theoretical van’t Hoff factor is 2. Deviations from 2 at higher concentration are primarily due to:

• Complete ionization of NaCl
• Ion pairing and electrostatic interactions between ions
• Errors in measuring molality only
• Change in water’s molar mass

Correct Answer: Ion pairing and electrostatic interactions between ions

Q50. Which observation generally signals a positive deviation from ideality in a binary liquid mixture?

• Measured total vapor pressure lower than predicted by Raoult’s law
• Measured total vapor pressure higher than predicted by Raoult’s law
• No change in enthalpy on mixing
• Zero excess Gibbs energy

Correct Answer: Measured total vapor pressure higher than predicted by Raoult’s law

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com